Retrofitting for Improving Indoor Air Quality and Energy Efficiency in the Hospital Building

Abstract

A growing body of research shows that retrofitting practices can potentially reduce energy demand in hospital buildings and enhance indoor air quality. Yet, there is a lack of comprehensive reviews associated with green retrofitting practices in hospital buildings. This study aimed to undertake a systematic review of the past literature on retrofitting techniques used to improve indoor air quality and energy efficiency in hospital buildings, to identify barriers to its uptake, and to recommend solutions to identified challenges. For this reason, a systematic review was conducted for the published research from various academic databases. Findings showed a growing uptake of various retrofitting strategies for indoor air quality in hospital buildings. As a result, hospital management or building owners might consider addressing these challenges to facilitate the uptake and implementation of retrofitting practices in their facilities.

1. Introduction

Hospital buildings and healthcare facilities account for a substantial amount of energy consumption and joint emissions [1,2,3]. Most hospitals operate 24 h a day, 7 days a week. During their operation, these facilities have extra requirements for waste management, imaging equipment, conditioning, clean air, and disease control [2]. Thus, healthcare buildings use a disproportionate amount of energy compared to similar-sized commercial or residential buildings [3,4]. In elaboration, hospital settings regularly require adequate air conditioning. According to Ji and Qu [3], during the past decade, the demand for energy for air conditioning has risen due to growing concerns about comfort in the built environment and indoor environment quality and an increase in ambient temperature.

A growing body of literature has also shown that the growing demand for electricity in hospital facilities is attributed to the demand for high-quality services and resource management [1,2,3,4,5,6,7]. For example, a wide variety of medical devices, ranging from large machines such as CT and MRI scanners to smaller ones such as nebulizers, can be found in healthcare facilities [5,7]. These devices all require electricity to function properly and promptly when required [5]. Refrigeration is used in hospitals to store laboratory samples, perishable food and drugs, and cadavers, among other sensitive products [6]. In addition, with a high proportion of aging building stocks, hospitals are among the least energy-efficient buildings [8]. Nematchoua et al. [9] explored energy consumption in hospital buildings and reported that the electricity consumption per square meter was twice as high as in other building types due to cooling and heating demands.

In developed countries such as Canada, the United States, and the United Kingdom, hospital facilities are reported to have the largest average annual thermal and electric energy consumption per floor area [10]. These findings show that, while energy is essential to the continued service delivery to hospitals, there is a widespread effort to decrease the amount of power used in these building environments. However, there are significant gaps between the aspirational goal of energy efficiency and the actual operation of buildings [5,9]. The current mitigation strategies are often implemented gradually and do not consider the whole-system approach to the problem to be effective [11]. Retrofitting hospital buildings has attracted growing research interest in overcoming high energy demand while improving energy efficiency and indoor air quality [12,13,14].

Retrofitting refers to changing the system or structure of a building after it has been initially constructed and occupied [12]. Retrofit renovations have the potential to enhance hospital building functionality while also enhancing the amenities available to patients and care providers [12]. Building retrofits have also been reported to significantly reduce the energy and water that hospital buildings consume as technology advances. In light of this, the current research aimed to investigate the most recent developments in retrofitting strategies and methods for reducing energy consumption in hospital buildings while ensuring indoor air quality.

Retrofitting entails incorporating new or updated components or equipment into an existing structure [12]. Over the past years, retrofitting has become increasingly popular to preserve existing facilities while making better use of redundant ones [12,13,14]. Retrofitting practices are relevant for hospital buildings, given that they are continuously changing in terms of the care delivery systems, methodologies, and technologies they utilize [13]. Researchers indicate that keeping up with the transformation through retrofitting is an effective strategy for reducing energy consumption and mitigating climate change through reduced greenhouse gas emissions [14]. While researchers have explored and documented the promising impact of retrofitting initiatives, there is no standard indoor air quality and energy efficiency strategy in all hospital buildings. Thus, there is a need to identify the most suitable energy-efficient retrofit measures to enhance indoor air quality and energy efficiency in hospitals.

Currently, the literature about retrofit measures in hospitals is unclear due to differences like service, priority, and commitment to change the status quo in energy consumption. Changing existing energy consumption practices has become essential, considering that building effects on the surrounding environment are becoming more apparent in global warming [13]. Most healthcare facilities understand that they are responsible for more than just their services and corporate profits. As such, they have attempted to implement sustainable practices and green buildings [15]. Yet, the number of existing retrofitting practices is limited, with management opting for new construction projects. Certainly, hospital buildings do not need to be new to be retrofitted and become efficient [16]. Therefore, retrofits for existing buildings can be cheaper than only focusing on undertaking new construction projects or creating new green designs [15]. However, there is debate about whether green building retrofits deliver proven results with minimal cost [14].

Proponents observe that, although retrofitting may not generate the attention-grabbing headlines typical of “trophy” construction projects, the pervasive impact they have had across the entire building landscape has helped raise the profile of sustainable building practices in the consciousness of the healthcare sector [14,15,16,17]. As such, adopting environmentally responsible practices should be more than a one-time event; rather, it should result in a discernible shift in how the healthcare industry is responsible for its day-to-day energy consumption operations [16]. To this end, the current study aimed to undertake a systematic review of past literature on retrofitting techniques used to improve indoor air quality and energy efficiency in hospital buildings and identify barriers to its uptake while recommending solutions to identified challenges. The study attempted to reach its objectives by answering the following questions:

• What retrofitting strategies are promising in improving indoor air quality in hospital buildings?
• What retrofitting strategies are promising in improving energy efficiency in hospital buildings?
• What challenges are experienced in facility attempts to embrace retrofitting?
• What measures are required to address existing challenges and enhance indoor quality and energy efficiency in hospitals in the future?

2. Energy Flows in Hospital Buildings

Power supply in hospital buildings is often complex and must adhere to strict regulations [17]. The focus on strict regulations is essential, considering that any change in performance could impact and interrupt other aspects [17]. For example, indoor lighting, ventilation, and air conditions are influenced by the functions and special activities of the given area or room it is designed for [18]. Once specific requirements and parameters are defined, it is essential to sustain the required indoor climate environment [18]. Poor design of these facilities regarding energy supply and backup systems could hinder the optimal operational efficiency of various hospital rooms and facilities designed to guarantee patient safety and well-being [19].

Moreover, hospital facilities are designed for long-term use, and in most cases, they are commonly utilized for more prolonged periods than planned [17,20]. During a building’s lifetime, frequently between 50 and 60 years, it is renewed and retrofitted several times to replace technical equipment [21]. Alternatively, the renewal may focus on developing new equipment, new energy-saving technologies or regulations, and improving different usages in specific settings [21]. The retrofitting also focuses on promoting sustainable fitting to the aging building. The common energy flows in hospitals include heating, electricity, compressed air, and cooling.

As to heating, the energy supply focuses on generating steam used in kitchens, sterilizing, and humidifying in heating, ventilation, and air conditioning (HVAC) [20]. Steam is used in transporting heat over longer distances. For example, hot water is often applied to central heating and tap water [21]. Electricity is used in hospitals to cool machines and for lighting, circulation pumps, air compression, HVAC fans, and running office equipment such as printers and medical equipment such as X-rays and CT scans [22]. In terms of compressed air, energy supply is used to direct the care and treatment of patients (i.e., surgical tools and breathing apparatus). Compressed air is often subject to very high standards of quality and availability for normal hospital operations to be sustained [21]. Additional compressed air is categorized as technical compressed air for keeping containers under pressure, workshop applications, and HVAC control systems [20,21]. Lastly, cooling remains another important aspect of energy supply in hospitals regarding climate control systems and for drying and cooling the ventilation air [20,21].

The HVAC system, Information and Communications Technology (ICT) data centres, and small personal power are among the largest electricity consumers in modern hospital buildings [22]. When compared to older buildings, newer hospitals typically have proportionately more air conditioning and a more extensive ventilation system [16]. The heating of rooms and the production of domestic hot water are the two primary uses of fuel [22]. Recent studies estimate that heating, ventilation, air conditioning (HVAC), and lighting account for between 50 and 60 percent of total electrical energy consumption [22].

As might be anticipated, healthcare facilities such as hospitals, clinics, and long-term care operations have specific energy requirements that are not typically met by other organizations [22]. As a result, there is a greater variation in the amount of energy that hospitals consume for a variety of reasons, including the use (general, psychiatric, health centre); the age and level of maintenance of the mechanical equipment; the level of the energy management; the climatic zone; the insulation level [16,20]; and retrofitting using architectural techniques (design-based strategies) and season of the year [21]. Consequently, there is an increased fluctuation in the amount of energy consumed by hospitals [16]. About 8% of healthcare facilities, such as health centres, consume 200 kWh/m² annually, 56% consume between 200 and 400 kWh/m², and 36% consume more than 400 kWh/m² [23]. In Europe, the average consumption is 295 kWh/m²/year; in North America, the annual average consumption ranges from 325 to 350 kWh/m²/year. Therefore, energy consumption differs by region.

Table 1. Characteristics of energy usage in hospital buildings.

No.	Setting	Usage
1	Indoor air quality	Internal air quality needs to be maintained in laboratories, intensive care units, emergency rooms, and operating rooms [24]. Critical areas require between 20 and 30 air changes an hour, with some rooms having special HVAC pressurization requirements [25]. Intensive care units, emergency rooms, and operating rooms often run over pressure to ensure protection and isolation from airborne infectious pathogens [26]. Quarantine rooms must have ultraviolent lights and negative pressure to achieve the goal of disease control and infectious isolation [27]. Achieving the desired indoor quality requires strict regulation of humidity, temperature, and quality; these requirements often increase the need for energy to achieve a proper cooling, heating, and fresh air environment [28].
2	High safety of energy supply	Because of their focus on patient care and concerns about legal liability, hospitals demand that power be available at all times. Investment in cogeneration, also referred to as combined heat and power or CHP, may be required depending on the circumstances. Backup generators contribute to an increase in operating costs [29].
3	Domestic hot water	To kill Legionella bacteria, domestic hot water needs to be heated to 708.8 °C. However, before water usage, the temperature must be lowered to 570 °C [30].
4	High-efficiency particulate air (HEPA)	It is necessary to have HEPA filtration installed in the ventilation system to stop the spread of the disease known as nosocomial infection. HEPA filters that have an efficiency of 99.7% place a greater demand on the electrical capacity of fans to ensure adequate air circulation [31].
5	Laundry facilities	Hospital facilities must also monitor peak demand hours from laundry and kitchen rooms because they are responsible for 10–15% of the total energy consumption of hospital buildings [32].
6	Climate control	To accommodate the adhesive cement used for orthopedics, the climate control in certain rooms must be set to 608 degrees Fahrenheit. This is because adhesive cement tends to set too quickly in warmer temperatures [33].

summarizes key aspects attributed to high energy use in hospital settings.

2.1. Energy-Saving Measures in Hospitals

A growing interest in ensuring energy efficient practices in hospitals emerges from the many activities and documents produced by private and public hospitals [23]. As a result, efforts are anchored on ensuring the best energy practices to facilitate consumption in most hospital facilities [34]. To achieve this goal, scholars and practitioners have recommended various energy-saving measures. For example, high-efficiency electrical motors with variable-speed drives can save up to 1–3% of the total electricity consumption [35]. Moreover, the use of Light-Emitting Diode (LED) lighting in hospitals and its contribution to energy efficiency has been recommended as another essential energy-saving practice [36].

Table 2. The summary of research conducted on energy saving measures in hospitals.

No.	Researcher(s)	Research Focus	Findings
1	Schicker, Spayde, and Cho [36]	Building combined heat and power (BCHP) technology and the energy efficiency of health facilities in rural settings.	Hospitals are the most promising structures for BCHP owing to the consistent thermal load demands that they have and the favourable heat-to-power ratio that they have.
2	Schüppler et al. [37]	An aquifer thermal energy storage (ATES) system was combined with a heat pump and installed in a Belgian hospital.	The primary energy consumption of the heat pump system is 71% less than that of a reference installation based on common gas-fired boilers and water-cooling machines.
3	Iqbal and Mohammad [38]	The contribution that fuel cells (FCs), photovoltaic (PV) systems, and solar thermal systems can make to hospitals, as well as the environmental benefits of installing such systems using a hybrid concept.	- Retrofit policies have the potential to offer a significant reduction in the number of green-house gases emitted. - The cost of the presented systems was the primary significant problem.
4	Li [39]	Solar-powered cooling systems for hospitals.	It is friendly to the environment and helps bring about a sizeable reduction in carbon dioxide emissions produced.
5	Bulté et al. [40]	Solar-powered cooling systems for hospitals.	Using solar-powered cooling ensures the total thermal and cooling load that originates from solar energy cuts costs, thereby ensuring collector performance.
6	Arabkoohsar and Sadi [41]	Solar-powered cooling systems for hospitals.	- A satisfactory portion of the loads could be covered when the solar-powered cooling system is around 500 m2 and the tank size is large enough. - The total annual savings produced by the system’s operation are quite sizeable, and the payback period for the system is 11.5 years if no additional funding is provided.
7	Rahman and colleagues [42]	Natural ventilation.	- Natural ventilation can deliver a much higher ventilation rate than mechanical ventilation in an energy efficient manner, thereby reducing the cross-infection of airborne diseases. - It is recommended that natural ventilation be used in appropriate hospital wards for infection control.
8	Bhagat and Linden [43]	Promotion of natural ventilation.	Along with significant initial expenses and managerial resistance, the healthcare facility’s location and immediate surroundings are also an underestimated barrier.
9	Sawyer et al. [44]	High indoor environmental quality impacts in hospitals.	The staff members complained of health problems that they believed were caused by the poor comfort conditions and air quality inside.
10	Patel et al. [45]	Environmental design to achieve energy efficiency.	Hypothesized that up to 70% of the net floor area of small to medium-sized health facilities could be naturally ventilated and that both staff and patients could benefit from more naturally sustained environments.
11	Arabkoohsar and Andresen [46]	Hospital energy demands and operational profiles using linear programming optimization methods.	- It was possible to optimize a combined heat and power system that was highly interconnected using linear programming optimization techniques. - The correlation between the local emissions of electricity and those of natural gas exerted a significant amount of influence over the configuration of the energy system. - The perception of satisfying comfort conditions could potentially lead to a reduction in the average number of patient-related health grievances and an improvement in the working conditions

summarizes the outcome of numerous research conducted on energy saving measures in hospitals.

Over the past few decades, there has been a significant advancement in information and communication technology for energy management in hospitals. The potential for the accomplishment of substantial energy efficiencies and savings in the working of existing hospital buildings was unveiled as a result of advancements in the operation, design, control, and optimization of energy-influencing building elements (such as natural ventilation, shading, CHP, FCs, solar, and HVAC) [47]. Building energy information systems (EIS), which emerged from the electric utility industry to manage time-series electric consumption data, address the problem of energy management for hospital buildings [48]. These systems were developed to manage time-series electric consumption data [45]. Advanced decision support methods and artificial intelligence have been incorporated to lower the amount of energy required by giving passive methods (such as shading, daylighting, and natural ventilation) the upper hand [45,48,49].

Additionally, other materials, such as phase change materials (PCM), which have already been used for other buildings, could be integrated into different construction elements to improve energy efficiency while simultaneously reducing the thermal mass of the building (in contemporary building constructions, thermal improvement approaches 62%). This would reduce the amount of heating energy initially required and cut down on energy in general [50,51]. Moreover, Hwang et al. [52] analysed the relationship between PCM and thermal comfort by examining the possibilities for energy-saving and enhancing indoor thermal comfort by installing PCMs with various attributes on rooftops over two time frames. Regarding the prospects of adopting innovative technologies and techniques in buildings, it is important to note that the most common problems are a lack of information and knowledge and a lack of economic incentives [53]. This is because most people do not have access to the necessary resources. Consequently, despite the challenging circumstances, the stringent regulations, and the requirement for continuous operation around the clock, recent studies unequivocally illustrate that the possibility of energy savings in health facilities is extremely high, with estimates ranging from 20% to 50%. Hospital organizations can implement these cost-cutting measures concerning the consumption of energy in two distinct but complementary ways, namely:

• Hospital buildings can be refurbished by adopting the most efficient and advanced technical solutions (such as efficient energy components, building services, and new materials).
• Users of various facilities in the hospital, such as nurses, medical staff, patients, and administrators, could be made aware of inefficient practices. Thus, these shareholders need to be trained more on the efficient use of energy resources within their clinical or workplace settings.

2.2. Retrofitting Strategies in Hospitals

Over the last decade, there has been substantial research on hospital energy efficiency practices to understand suitable retrofitting methods to reduce energy consumed in this industry.

Table 3. Retrofitting strategies in hospital buildings.

No.	Researcher(s)	Research Focus	Findings
1	Heye, Knoerl, Wehrle, Mangold, Cerminara, Loser, Plumeyer, Degen, Lüthy, and Brodbeck [53]	Energy consumption in CT and MRI operational rooms in Switzerland.	- Inadequate air change rates result from blocked air-exhaust vents, poor maintenance of the installation, and insufficient staffing in technical departments. - The auditing operation revealed significant noise and inadequate indoor lighting issues.
2	Guzović et al. [54]	Implementing a pinch technology.	- Implementation of pinch technology can reduce the amount of thermal power consumed by as much as 39%, simply by including four heat exchangers in the system. - The energy saving was equivalent to saving 246 thousand litres of diesel fuel.
3	Miecznik and Skrzypczak (2019)	Investigated two healthcare facilities in Poland with 470 beds regarding the seasonal shifts in the heat required to generate hot water for household use.	- For both hospitals, the heat consumption was at its highest between 8:00 and 19:00, while it was at its lowest between the hours of 1:00 and 6:00. - The results of the measurements are helpful for forecasting a new hospital facility during the design process or for assessing the economic viability of using clean energy sources such as solar heating or energy recycling.
4	Tam et al. [55]	Investigating the flux of usable energy and the coefficient of energy conservation of an incinerator used for the combustion process of medical waste in an Oncological Hospital in Hong Kong.	- Plastic was considered the primary contributor to the total waste mass. - The impact of the dirt produced during the burning process: as a result, the steam temperature increased while the pressure decreased, and the incinerator’s overall efficiency was reduced. - Nearly 660–800 kW of usable energy could be obtained from 100 kg of medical waste; the hospital could also sell the saturated steam produced by the incinerator as a standalone product to increase its revenue. - Steaming and shredding, which require less energy and produce far fewer carbon gases, are thought of as another justification.
5	Renedo et al. [56]	Various possibilities for domestic hot water use, cooling, and heating in local hospitals in Santander, Basque Country, Spain.	- The technologies suggested for improving its energy efficiency included various combinations of CHP technologies such as gas turbines, diesel engines, and absorption chillers. - Using a CHP system can potentially lessen the electrical disturbances brought on by the power utility, thereby increasing the time that medical equipment is expected to remain functional.
6	Vanhoudt et al. [57]	An aquifer thermal storage system in a Belgian hospital: Long-term experimental evaluation of energy and cost savings.	- Compared to a conventional installation, ATES resulted in savings of up to 71% in primary energy consumption. - The installation of the suggested system could result in savings of EUR 54,000, with the payback period estimated at 8.4 years.

below illustrates the summary of the research conducted on retrofitting strategies in hospitals.

3. Materials and Methods

The purpose of this study was to understand retrofitting strategies that could be used to improve indoor air quality and ensure energy efficiency in hospital buildings. The purpose of this chapter is to provide specific information regarding the research methods and approaches utilized to collect pertinent data to respond to the research aim and questions. A secondary research design was used in the current study to collect relevant resources on the subject of indoor air quality and energy efficiency in hospital buildings and publications on various retrofitting methods [58]. Various sources were reviewed to conduct a comprehensive and in-depth analysis of the subject matter, including academic databases and institutional websites. The study used various academic databases, including Science Direct, Google Scholar, the Wiley Online Library, Research Gate, and SAGE. The following section provides a more in-depth description of the search parameters used to locate relevant research by searching academic databases, institutional catalogues, and government websites.

3.1. Search Criteria

Different phrases, keywords, or search terms were used to identify suitable resources related to retrofitting methods in hospital buildings. A comprehensive search of the literature was conducted through these different search terms. The keywords were used alone or in combination with other phrases to achieve a detailed and comprehensive search process. Some of the used keywords included “energy demand”, “healthcare facilities”, “refurbishment”, “retrofitting and indoor air quality”, and “retrofitting and energy efficiency”. Additional keywords included “hospital ventilation”, “healthcare energy engineering”, “energy efficiency retrofit strategies”, “retrofitting and ventilation”, retrofitting and indoor comfort”, and “operative temperature”.

During the investigation, several publications with titles containing related key terms and research objectives comparable to energy-efficient practices and retrofitting were discovered. However, due to the various search engine optimization strategies employed by the utilized academic databases, there could have been variability in the search terms, phrases, and keywords used. A combination of various keywords was performed to thoroughly search the relevant resources required for the study.

3.2. Inclusion and Exclusion Criteria

To select relevant resources for the study, specific criteria were followed to include relevant studies and exclude others. The criteria used were centred on the year of publication, the language, and the subject or theme. Only studies that were published between the years 2002 and 2022 were considered for inclusion in this study. The choice for the 20 years was informed by the need to comprehensively search the past literature to understand retrofitting strategies developed over the years to improve indoor air quality and achieve energy efficiency in hospital buildings. Only English-language publications were factored into the study. The current study did not include book reviews, systematic reviews, opinion articles, archival data, magazines, or other non-academic documents.

The initial search of relevant studies on the topic identified 531 studies from academic databases. Examining the resources using their abstracts, titles, and executive summaries resulted in the exclusion of 152 duplicates, thereby remaining 379 studies. After further analysis, 394 studies were excluded; 182 were screened and removed because 78 were not related to retrofitting in hospital buildings, 44 studies only had abstracts/summaries, 25 were opinion articles, 22 were periodical letters, and 13 were non-English articles. Out of the 197 fully screened studies, 95 were excluded since they covered retrofitting in commercial buildings, and 39 covered the retrofitting of structural problems unrelated to energy use or indoor air quality. We included a total of 63 studies (Figure 1) in the final systematic review.

3.3. Data Coding and Analysis

The responses from 63 studies were analyzed using a thematic approach. The thematic analysis relied on the qualitative evaluation and interpretation of primary funding to provide significance and meaning to the investigated phenomenon. In this study, the thematic analysis involved categorizing interview data and secondary source information into similar meanings, assigning themes, and identifying common patterns in the data. The document analysis of the 63 studies consisted of coding and thematic analysis steps. The analysis processes included familiarizing with the raw interview and secondary data, open coding of essential information, generating significant themes from open coding, reviewing themes to ensure they aligned with the research objective and questions, defining themes, and writing findings.

4. Data Findings

The current section presents results from 63 studies related to retrofitting practices for improving indoor air quality and achieving energy efficiency in buildings. Results are discussed in light of the formulated research objectives. The section first identifies retrofitting strategies that improve hospital building indoor air quality. Then, specific retrofitting methods that offer promising outcomes for improving energy efficiency in the hospital building are detailed. Potential challenges experienced in facility attempts to embrace retrofitting are discussed, followed by an outline of measures required to address existing challenges while enhancing indoor quality and energy efficiency in hospital buildings in the future.

4.1. Retrofit Methods to Improve Indoor Air Quality

The first objective was to understand the following: What retrofitting strategies are promising in improving indoor air quality in hospital buildings? Findings from 21 studies [59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80] identified multiple ways to increase ventilation and air changes per hour (ACH) in hospital buildings. The basic methods of improving indoor air quality, which does not often consume energy, include source control and opening windows [59,66]. Source control is the most effective way to improve indoor air quality since it reduces or eliminates individual sources of pollution [66,68]. For example, potential sources of pollution, such as those containing asbestos, could be retrofitted with greener tiles and other roofing methods [68]. Besides, sources of pollution can be enclosed or sealed, while others, such as gas stoves using fossil fuels, can be adjusted to reduce emissions [67]. Source control is often more cost-effective for protecting indoor air quality than increasing ventilation since increasing ventilation can increase energy costs [68,70,72].

A total of 15 studies identified that hospitals could improve indoor air quality by using filters, installing ultraviolet germicidal irradiation (UVGI) systems, and upgrading to more efficient HVAC systems [60,61,62,63,64,65,71,72,73]. Such an approach focused on increasing air changes per hour by employing different control strategies is commonly referred to as “equivalent” or “effective” air changes per hour (ACH) [60,70,71]. Retrofit measures related to upgrading air handling units focus on enhancing the circulating room air in hospital rooms [70]. Air handling units could use (1) filters or (2) germicidal ultraviolet lamps. To effectively remove smaller particles, filters should have Minimum Efficiency Reporting Value (MERV) ratings greater than 8 per ASHRAE recommendations [71]. A filter’s MERV rating indicates how effectively it removes airborne particles [71]. The higher the MERV rating, the more effective the filter captures particles. As an illustration, the filtering capability of the media used in a MERV 16 filter is comparable to that of the media used in an N95 mask [72]. Alternatively, a MERV 16 filter can capture 95% of particles between 0.3 and 1.0 microns [72]. In the case of germicidal ultraviolet lamps, their use substantially reduces the number of bacteria accumulated or buildup in systems, thereby improving overall indoor air quality.

UV fan retrofit presents another option where HVAC could be improved, which could help ensure overall air quality. Nonetheless, critics observed that UV fan retrofits may not help reduce the transmission of disease-causing pathogens, especially in smaller, enclosed spaces [72]. Based on the fan’s CFM rating, well-designed UV fan units usually include an ACH-effective additive [73]. Light progress UV fans have been noted to effectively ensure hospital indoor air quality. The light fixture circulates and purifies the air in a room using TiOx filters and UVC lamps [61]. As low-level sound equipment, the UV FAN operates at 44 decibels by circulating air while reducing the contaminant load by 99.9%. Because the UVC is encased, its installation is safe and simple, with low energy consumption [61].

Upper-air UVC retrofits also contribute to important retrofits in enhancing indoor air quality. The use of upper-air UVC fixtures in hospitals and other healthcare facilities has been growing, especially in bacterial and viral control, such as in tuberculosis wards [62,74]. Upper-air fixtures employ louvres to direct UVC into the room’s upper region [75]. The UVC disinfects the area in the room’s upper portion. The room is eventually sanitized due to air changes per hour (ACH) [76]. Upper-air units that are properly designed and applied increase the effective ACH (ACHe) in hospital rooms. The units generate an ACHe 3–10 times the mechanical ACH in a given space, with up to 40% less energy consumption [74]. Thus, the impact of these retrofits on indoor air quality may be considerably greater. Upper-air UV-C units are an additional excellent option for cleaning the air in smaller, enclosed spaces such as dressing rooms, waiting rooms, patient wards, and doctors’ appointment rooms [62,76]. Multiple variables, such as louvre direction and reflective surfaces, need to be considered to ensure the proper operation of upper-air fixtures, thereby necessitating the need for commissioning [76].

The use of ceiling fans further presents a simple retrofit measure that may substantially improve the hospital buildings’ resilience to indoor air quality, even in extreme seasons [77]. Additionally, the outdoor air quality could enhance and promote quality air in several ways. One includes using natural ventilation via doors and windows [78]. Second, mechanical means could also be used, such as outdoor air intakes associated with heating, ventilation, and air conditioning (HVAC) [79]. Third, hospital buildings could also use infiltration, where the outdoor air flows into the interior spaces through cracks, joints, openings, ceilings, and floors and around doors and windows [63,64,65,80].

4.2. Energy Efficiency

The second objective was created to help identify the following: What retrofitting strategies are promising in improving energy efficiency in the hospital building? Findings from 33 studies showed nine potential strategies that could be retrofitted to hospital buildings to enhance energy efficiency [81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112]. These retrofit measures focus on the real-time visibility of energy uptake, water efficiency, and continuous commissioning of HVAC. Other measures include virtual building automation, public engagement and visibility, space utilization, load curtailment, green roofs, and maintenance and operations.

Real-time visibility is needed to ensure energy efficient operations [81]. Most hospital buildings offer little to no visibility into the real-time energy use of the building’s various parts. In today’s world, where real-time services and products are the standards, it is unproductive to manage energy consumption on a monthly utility bill [82]. The healthcare industry may be committed to energy saving; however, they lack the necessary tools to execute [81,84]. Using Internet of Things retrofits could help hospitals make routine assessments of how they consume energy at the entire building level and individual departments. Thus, hospitals need to move beyond each department’s main utility meter and submeter and integrate it with Building Automation Systems (BAS).

Implementing a building management system (BMS) is an efficient way to reduce energy loss because it provides a better understanding of current practices and aids in making better decisions. BMS is one of the first strategies to consider when evaluating energy efficiency and water consumption [113].

Water efficiency is a potential issue affecting hospital buildings’ energy consumption. Cooling towers consume up to 40% of energy, and retrofits of greener initiatives such as solar panels could reduce electricity use by up to 10–20% and thermal energy demands by up to 35% [85]. The average daily water use can reach hundreds of thousands of gallons. Without real-time insight into the cooling tower operation (e.g., blowdown, system leaks, and drift), a building cannot claim to have implemented green building techniques [86]. To achieve genuine water efficiency, low-cost Internet of Things retrofits can give necessary insights through asset digitalization of the chiller and the cooling tower [87].

Scheduled performance reviews on HVAC equipment are not always synonymous with recommissioning [88]. The HVAC system’s performance degrades with time. Inadequate building maintenance or alterations in the structure’s function can lead to inefficiency [89]. Once comfortable, building spaces can become inadequately or excessively cooled/heated, resulting in occupant complaints. Energy efficiency would deteriorate in such a situation [88]. Continuous design and construction codify the procedure of guaranteeing that your HVAC system is operating at maximum efficiency [89]. This ongoing procedure aims to resolve operational issues, enhance tenant comfort, and maximize energy consumption in existing buildings [89]. Continuous commissioning could also extend the service life of HVAC equipment. Continuous commissioning saves the efficiency of the HVAC system and contributes to a 20% reduction in energy demand.

Sala, Alcamo, and Nelli [83] set out to demonstrate that there are substantial possibilities for lowering energy consumption in the European hospital sector, thereby contributing to a substantial reduction in CO₂ emissions. The primary objectives were incorporating energy efficiency strategies in the hospital sector, following current regulations, intending to enhance environmental quality and the ecosystem, and promoting sustainable natural resource management [83]. Innovative strategies such as HVAC for incorporating renewable energies into buildings have been combined with bioclimatic design to improve building management, energy efficiency, thermal comfort, natural ventilation, and daylighting. In addition, using greener energy alternatives such as photovoltaic modules, high-efficiency heat pumps, integration with the surrounding green areas, and incorporating indoor vegetation potentially contributes to a 27% reduction in energy demand and enhances patient comfort.

According to research by Cesari, Valdiserri, Coccagna, and Mazzacane [93], retrofitting with different glazed windows reduces the air conditioning load and energy consumption. The investigation focused on the selection of windows from economically feasible products, with the intention that property managers select a reasonable model of glass from the market based on the analysis results to reduce the property’s energy consumption. Using modelling techniques, Chirarattananon and Taweekun [94] discovered that LED lighting reduces energy consumption by 20–40% in hospital buildings when combined with the control method. Gomes, Rodrigues, and Natividade [95] investigated a six-story hospital building and found that modifying the lighting type could result in annual savings of 56–62% and decarbonization of nearly 3 tons.

When using thermal insulation in exterior walls and roofs, the HVAC system consumes approximately 40% less energy, significantly reducing operating costs. Sadek and Mahrous [97] hypothesized that system efficiencies (appliances, lighting, and HVAC) and tenant practices (e.g., equipment used and temperature swings) are distinct as primary energy consumption variables, each with a potential of approximately 30% compared to existing conventional workplaces. As such, the researchers suggested that feasible strategic plans need to be retrofitted in hospital buildings to promote energy efficiency [98,99] and energy conscious behaviour patterns [100], which, when combined, could halve the energy requirements of the modern hospital working environment.

Installing a green roof refers to special-purpose roof installation promoting vegetation growth (e.g., grass, plants, flowers, bushes, and other forms of vegetation) on rooftops [101,102,103]. Implementing green roof technology in an urban setting can result in numerous benefits [102]. A green roof, for instance, can reduce site-level stormwater runoff, decrease hospital buildings’ heating/cooling energy demand, and reduce the urban heat island effect caused by large hospital buildings [103]. The popularity of extensive green roof systems has increased due to their lightweight, low-cost, and low-maintenance requirements [101,103]. Green roofs easily check the sustainability box for hospital buildings.

Although the design and construction of a building may have emphasized sustainability, it can only remain so if it is operated and maintained responsibly [104,105,106]. Several design strategies can be considered for energy efficiency in buildings, including hospital buildings, as described by Walker [114], such as:

• Natural ventilation: Utilizing natural ventilation strategies such as operable windows, skylights, and other openings to allow air to flow through the building can reduce energy costs associated with heating and cooling.
• Passive Solar Design: Incorporating passive solar design strategies such as orienting the building to maximize solar gain, using light-colored materials on the roof and walls, and incorporating shading devices can reduce energy costs associated with heating and cooling.
• Insulation: Installing insulation in walls, ceilings, floors, and other building areas can reduce energy costs associated with heating and cooling by reducing air leakage.
• Air Sealing: Sealing air leaks around windows, doors, ducts, pipes, and other building areas can reduce energy costs associated with heating and cooling by reducing air leakage.
• High-Efficiency HVAC Systems: Installing high-efficiency HVAC systems such as heat pumps or geothermal systems can reduce energy costs associated with heating and cooling by using less energy to achieve desired temperatures.
• Heat Recovery Ventilation Systems: Heat recovery ventilation systems (HRVs) can reduce energy costs associated with heating and cooling by recovering heat from exhaust air before it is vented outside the building.

Energy efficiency diminishes utility costs for building owners but disregards the condition of the power grid. Green hospital buildings can participate in load curtailment or demand response programs, which decrease electricity consumption for brief periods to assist the power grid during peak demand periods. Participants in load reduction programs often receive substantial compensation for load shedding on demand. Extending internal energy generation and conservation initiatives such as solar energy could reduce energy costs for healthcare facilities, thereby contributing to overall system efficiency.

4.3. Barriers to Uptake of Building Energy Retrofitting

The third objective was created to help understand the following: What challenges are experienced in facility attempts to embrace retrofitting? Findings from eight studies identified four key barriers to the uptake of energy retrofitting practices in hospitals [115,116,117,118,119,120,121,122]. These barriers are related to economic, regulatory, knowledge, and social hindrances. Economic barriers include uncertainty about financial returns, lack of materiality, cost reduction, split incentives, price signals, priority in investment focus, high initial costs, and lack of finances [115,117,119,120]. In terms of lack of finances, the hospital building owners may lack sufficient funds to retrofit rooms with desired energy-efficient technologies or innovative air quality techniques. Initial costs are also high, with benefits taking time to accrue, implying long payback time and, thereby, a lack of commitment to retrofit these hospital buildings [116].

Building owners may also have different financial priorities, such as investing capital in high-return ventures preceding retrofitting commitments [116]. If price signals for retrofits promise higher returns, there is an increasing commitment to investing in energy saving programs within hospital settings. Similarly, split incentives imply that building owners may be less willing to pay for retrofit costs if the incentive fails to guarantee full benefits [117]. When cost minimization becomes an essential austerity measure, there is an increased likelihood of cutting costs for energy efficiency programs such as retrofits [117]. Potential uncertainties concerning retrofitting in terms of actual and predicted energy saving could influence commitment to this program [118]. Lastly, the incremental investments from retrofitting are relatively small compared to the returns from other investments, and as a result, they receive less consideration [119].

Regulatory barriers also present a challenge when investing in retrofitting programs. These barriers relate to a structural, institutional, fragmented market, multiple stakeholders, and poor governance [119]. In terms of a fragmented market, there are concerns that, in most cases, none of the professionals (during the operation, construction, and design phases) is an expert in building energy efficiency. Still, they share the responsibility for achieving it, posing a coordination challenge [119]. There is a preference among institutional investors who are more acquainted and familiar with larger-scale financing and supply-side investments over smaller (often considered “riskier”) demand-side projects [120].

Regarding structural issues, there are concerns that the average age of the building stock is increasing due to a low demolition rate. The landlord–tenant dilemma makes it difficult to improve the existing building stock due to the age of the structures [120]. Poor governance could also derail retrofitting projects, considering that a lack of strong commitment to policies that encourage greener energy practices could negatively impact reforms in the healthcare industry.

Knowledge barriers also contribute to the slow or lack of uptake of retrofitting programs in hospital settings. Key issues of concern include lack of motivation, knowledge about energy-saving potential, lack of awareness and information access, confusion about the best option, negative perceptions about green energy programs, and poor skills in retrofitting technology [116,118]. Often, sustainability is poorly understood by consumers and building owners. In some instances, they are unaware of the current best practices and do not fully grasp the efficacy of energy efficient technologies [120]. Despite widespread agreement that conserving energy is essential amid climate change and global warming, there is still a lack of knowledge regarding carbon, cost, and energy savings from various strategies, making it difficult to select the optimal choice.

Some building owners are not interested in improving their properties unless there is imminent danger to the building’s equipment or an alarmingly high degree of vacancy that negatively impacts the owner’s rental income [121]. There are skill shortages in the contractor sector that is responsible for the appropriate installation of energy-saving solutions and in professional services, where few designers and architects are conversant with environmentally friendly retrofitting renovations [121]. When multiple professionals give contradictory recommendations regarding the best retrofitting approach, such an issue may cause consumer skepticism regarding installing energy efficient measures [121]. Negative perceptions by some building owners that investing in retrofitting could not provide desired returns often create concerns about continuous financial burden and demand for regulatory compliance [121].

4.4. Energy Conservation Techniques for Hospital Buildings

The fourth objective was created to understand the following: What measures are required to address existing challenges and enhance indoor quality and energy efficiency in hospitals in the future? Findings show that, as organizations safeguard public health, hospitals are accountable for preventing an environment of excessive energy usage and cost [104]. Several case studies summarized in this review showed that the expense of these high-tech devices continues to be an insurmountable obstacle to their widespread deployment [11,16,104]. Simple energy conservation strategies (for which no special budget should be required) can reduce primary energy use by between 10% and 20%. High-cost energy groups should be targeted and tracked to identify areas where potential savings might be realized using an interconnected energy management program.

It is evident from the preceding discussion that there are several technical approaches for enhancing hospital energy efficiency in the future. As a proposal, the technicians and engineers should explore the more straightforward retrofitting procedures [22]. Frequently, moderate investments and improved maintenance and operation methods can result in immediate and long-lasting energy savings. Low-cost actions, such as resetting timers and turning off appliances (heaters, lights, etc.) in unoccupied rooms, remain the most desirable [104]. In addition, practical advice for energy conservation in hospitals includes focusing on lighting, heating systems, CHP, building fabric, and air conditioning [16,36]. Lastly, sophisticated surveillance and power management algorithms discover faults and recommend further enhancements [1,2,3,4,5,6,7].

In the future, the focus should be on retrofitting heating systems by optimizing the energy uptake of room thermostats, boiler replacement, installing local water heaters, insulating boilers and tanks, and working on effective thermostatic radiator valves [104]. CHP could also be enhanced to reduce energy uptake by carefully checking the electricity and heating needs and ensuring all electricity and heat that are used within the hospital building [43]. As applies to AC and building fabric, there is a need to undertake window shading, draught proofing, and insulating roofs [58,123]. Lighting could be optimized in several ways, including replacing incandescent tungsten lamps with compact fluorescent lamps, using low-energy tubes instead of fluorescent ones, using electronics to replace existing electromagnetic ballasts, and evaluating the applicability for daylight competitors, presence of a detector, and time controls.

Future improvements to enhance indoor quality and energy efficiency in hospital buildings could also be achieved by exploring possibilities for heat recovery from exhaust air, using natural air for free cooling, and enhancing control settings [9]. Considering the need for beam heating and air conditioning, they could improve energy management systems and ensure that all possibilities have been assessed to make better use of retrofitted systems [104]. Maintenance could also ensure the sustainability of energy efficient practices where the focus could be on making regular system interventions, components, and equipment upgrades. A schedule for maintenance and inspection could also ensure energy-efficient practices [104].

5. Conclusions

As the problem of global warming increases due to greenhouse gas emissions, hospital management continues to show a growing commitment to reducing energy consumption in their facilities, while ensuring optimal indoor air quality for staff and patients. Findings from this review show constant efforts by various hospitals to adopt different strategies geared towards reducing energy consumption in their facilities. However, there is a lack of a uniform approach regarding how energy could be optimally conserved and how indoor air quality should be achieved and sustained. Instead, strategies used by hospitals differ based on access to various energy resources and their geographical location. While some hospitals focus on using greener energy, such as solar and geothermal, others still use costly thermal energy that further contributes to global warming. Thus, there is a need to explore whether and how retrofitting could be used in the healthcare industry to address energy conservation efforts in hospital settings.

A review of 63 studies drawn from various academic databases showed that indoor air quality could be improved by eliminating individual sources of pollution. Retrofitting using greener materials such as tiles and other roofing methods could eliminate asbestos hazards and avoid energy-consuming ventilators. Air quality could also be improved using filters, installing ultraviolet germicidal irradiation (UVGI) systems, and upgrading to more efficient HVAC systems. Retrofitting rooms with air handling units such as filters and germicidal ultraviolet lamps could improve overall air quality. Similar outcomes could be achieved using upper-air UVC retrofits and mechanical means such as outdoor air intakes or infiltration via joints, openings, ceilings, doors, and windows.

Energy efficiency in hospital buildings could be achieved using retrofit measures that focus on the real-time visibility of energy uptake, water efficiency, and continuous commissioning of HVAC. Additional energy-conserving retrofits could include virtual building automation, optimal space utilization, load curtailment, green roofs, and maintenance and operations. While these retrofitting methods could lead to a substantial decrease in energy consumption, findings showed potential barriers to their uptake. These barriers include inadequate funding or budgetary allocation, regulatory problems, lack of knowledge and expertise, and social concerns. In the future, hospital management or building owners might consider addressing these challenges to facilitate the uptake and implementation of retrofitting practices in their facilities.

Technicians and engineers need to explore more straightforward retrofitting procedures. The focus should be on making moderate investments in immediate and long-lasting energy-saving retrofitting techniques. Low-cost actions, such as resetting timers and turning off appliances (heaters, lights, etc.) in unoccupied rooms, remain the most desirable retrofit approaches. In addition, practical advice for energy conservation in hospitals could include mitigating energy demand for lighting, heating systems, CHP, building fabric, and air conditioning. Installing surveillance and power management systems could help in the early identification of potential faults, thereby giving timely support to decision processes on suitable retrofitting recommendations for better indoor air quality and energy efficient practices.